What color primer for going under red?

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Tool box has paint peel on the front panel directly below the bottom drawer. Factory paint is directly over bare steel using no primer. I've been able to match the factory color with factory paint as long as I don't use primer underneath. But now the repaint if flaking off after about 5 years. I'm assuming the repaint is not grabbing a hold of the bare steel as well as I had hoped. The section I'm going to paint is about 3 inches high by 33 inches wide. Also, what grit sand paper for the bare steel before primer? I got plenty of time to think about it since the weather is not quite warm enough anyway. Just throwing this out there.
 
I need something with lots of contrast just so I can see. I would probably use gray. I use lots of red oxide spray primer under black just so I can see thin spots. My sandblaster uses gray primer on wheels and I shoot Dove gray, it can be really frustrating.
 
Gray is usually SOP. Now, PPG and Axalta on the transportation side of things have been going “keyed” shades of gray/black/white with their AChromatic/ValueShade primers in the formula notes, while the trend for house paints is gray primer under “deep” colors.
 
I like to use black, only because it gives the red a deeper color, on my opinion.

You also asked on what grit sand paper... I would use a roloc cookie, as light of grit as possible, but enough to remove contaminations like rust, and to make a smooth transition area. If you have no rust, you might use on of those green roloc pieces, they do not remove metal (anything tangible) and do a great job of cleaning.
 
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You'd have to compare the reflectivity of the two primers to find out. My guess is beige would be okay. I'd avoid very bright or very dark primer.
So then in that case, a white primer might make the red look pink? That's a scary thought.
 
So then in that case, a white primer might make the red look pink? That's a scary thought.
No, it's not like color mixing. White primer will make the color look brighter and more vibrant. Dark primer will make the color look darker. Some colors look better with black primer. I'm not sure if this is done in the case of vehicles but in scale model building, you want to use a black primer under a silver finish because it makes the silver pop.
 
No, it's not like color mixing. White primer will make the color look brighter and more vibrant. Dark primer will make the color look darker. Some colors look better with black primer. I'm not sure if this is done in the case of vehicles but in scale model building, you want to use a black primer under a silver finish because it makes the silver pop.
Black primer makes the silver pop? Wow! I would've never thought that.
 
Black primer makes the silver pop? Wow! I would've never thought that.
Black primer makes silver look darker and gives the appearance of more depth. Generally, I’d say use light primer with light colors, a grey primer with medium bright colors, and a dark primer with dark colors. If you want to brighten or darken a color you can do that by choosing a lighter or darker primer. Of course, how thick you spray the paint over the primer also affects the appearance of the color.
 
Black primer makes silver look darker and gives the appearance of more depth. Generally, I’d say use light primer with light colors, a grey primer with medium bright colors, and a dark primer with dark colors. If you want to brighten or darken a color you can do that by choosing a lighter or darker primer. Of course, how thick you spray the paint over the primer also affects the appearance of the color.
My main concern is too much build up on the inside corners. Those inside corners are the dead giveaway. That's one reason why I skipped the primer the last time.
 
A "red lead" red oxide primer which has a brownish tint for lack of a better term and would work nicely. This works very well. Red Oxide Primer You can use either a fine or medium grid Scotch-Brite sanding pad to sand it, Sanding pad. You don't want to use something too coarse you might see where you sanded through the surface after it is finished. Make sure there is no oil or grease on it prior to sanding, and priming painting. Clean it well after sanding.
 
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What topcoat are you actually using.
That would be and I quote : "Custom Products Corporation REP-12A Red Acrylic Enamel. Net Weight 12 Ounces."

I've used it before and it's a perfect match as long as I spray it over bare metal.

If I try to spray it over dried and cured light grey primer, it doesn't match. I ordered it from Snap-on.
 
What about etching the steel with phosphoric acid rather than priming it? Etching will improve adhesion and will barely affect the color compared to bare steel. Also, we are talking about partially repainting a tool box and not a Bugatti.
 
What about etching the steel with phosphoric acid rather than priming it? Etching will improve adhesion and will barely affect the color compared to bare steel. Also, we are talking about partially repainting a tool box and not a Bugatti.
I don't know about etching it with phosphoric acid, but the people on YouTube say that a top coat cannot be sprayed over an etching primer because if it is, the etching primer will lift up the top coat. They say the etching primer must be first neutralized with a coat of primer sealer.
 
I don't know about etching it with phosphoric acid, but the people on YouTube say that a top coat cannot be sprayed over an etching primer because if it is, the etching primer will lift up the top coat. They say the etching primer must be first neutralized with a coat of primer sealer.
The chemistry of the etching primer may be incompatible with the top coat. If you etch the steel with acid you will then neutralize the surface by washing it with water and ammonia. I don’t want to give you any incorrect advice.
 
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